REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR IN CARDIAC MYOCYTES

Collateral blood vessels supplement normal coronary blood flow and cor onary blood flow compromised by coronary artery disease, thereby prote cting the myocardium from ischemia. Collateral vessel formation is the result of angiogenesis. Vascular endothelial growth factor (VEGF), al so known as vascular permeability factor (VPF), is a secreted mitogen specific for endothelial cells and an extremely potent angiogenic fact or. In the present study, VPF/VEGF mRNA and protein were demonstrated to be markedly stimulated in primary rat cardiac myocytes in vitro in response to reduction of the oxygen tension to 1% or inhibition of the electron transport chain. Four isoforms of VPF/VEGF were coordinately regulated by hypoxia, including a novel isoform not previously descri bed. Phorbol ester and the depolarizing agent veratridine, stimulators of protein kinase C and calcium influx, respectively, were found to m arkedly increase VPF/VEGF mRNA expression in cardiac myocytes. Forskol in, a potent stimulator of adenylate cyclase, produced a small but sig nificant increase in VPF/VEGF mRNA expression in the cardiac myocytes. However, only H7, an inhibitor of protein kinase C, inhibited the hyp oxic induction of VPF/VEGF mRNA; inhibitors of calcium influx and the calcium-calmodulin-dependent protein kinase II as well as inhibition o f protein kinase A did not block the hypoxic induction of VPF/VEGF mRN A. This suggests that more than one signal transduction pathway is inv olved in regulating VPF/VEGF expression. The sensor that regulates the expression of hypoxia-responsive genes has been proposed to be a heme protein. Consistent with this model, transition metals initiate a gen etic program similar to hypoxia. In the present study, the transition metals cobalt and manganese increased VPF/VEGF mRNA in cardiac myocyte s in vitro and myocardial tissue in vivo, providing evidence that a si milar sensor may regulate VPF/VEGF in the cardiac myocyte. These data suggest a novel mechanism by which VPF/VEGF induction contributes to c ollateral vessel formation in ischemic myocardium and also suggest str ategies to increase VPF/VEGF production in vivo.